Computer data to be stored on removable media is typically arranged in data volume units that originally corresponded to one data storage media, such as a reel of tape or tape cartridge or cassette, or an optical disk or cartridge. The capacity of such storage media has grown substantially in recent years. Thus, the average size of data sets in most computer or data processing centers is significantly less than the capacity 5 of the data storage media volumes. Most programming support for peripheral data storage is directed at only the original volume units and does not provide a general solution to storing multiple data sets in the same volume. Consequently, a development for better utilizing the full capacity of a removable media cartridge (also called a media volume or a physical volume) is to store multiple volumes (called virtual or logical volumes) on a single physical volume in a stacked fashion. Data which would have been stored in multiple, mostly unused physical volumes are collected and stored on a single physical volume in separately addressable, host-processor defined logical data storage volumes. The '557 patent describes the creation and management of such logical volumes and the associated physical volumes in an automated virtual storage and retrieval library. As the result, the host processor treats only logical volumes as though they were separate physical media volumes, and the library manages the access to the logical volumes by accessing the associated physical volumes. A subsystem providing automatic management of tape data storage having such logical volumes is called a virtual media server. As can be appreciated, the management of contention for disparate logical volumes on the same physical volume can be very difficult. The patent incorporated by reference is directed to providing solutions to these problems by such a virtual media server and a library manager. The patent describes establishment of stored tables of logical volume records and of physical volume records for managing the data storage.
Presently, the typical number of logical volumes contained in a single physical volume is approximately 50. The number of cartridges stored in storage cells in a typical tape library may be 1,000, with the result that a typical virtual media server tape library, such as the IBM 3494, contains 50,000 logical volumes. Management of a virtual media server database for tracking the logical and physical volume relationship is accomplished by the virtual media server. Each of the physical volumes and its stacked logical volumes is stored in a library storage cell which is accessed by an accessor robot and delivered to a data storage drive. Operation of the library accessor is controlled by a library manager. Management of a library manager database is accomplished by the library manager for tracking the physical volumes and the storage cells.
Often, a host system will expire the data in a logical volume when it is superseded by subsequent data, or upon an administrator providing a command indicating that the data is no longer needed. It would be advantageous for the host system to "eject" the logical volume, and delete the expired logical volume from the databases, reducing the size of the databases. However, because of the fact that the logical volume is tracked by multiple databases, including databases in the host system, by the virtual media server database and by the library manager database, and there is no ability to determine whether the logical volume is clearly inactive to any host system, any attempt by a host system to eject the logical volume is currently rejected by the library manager. Thus, even though no active data is contained in the logical volume, it remains in the databases.
The only ability to eject or delete a logical volume is if the volume is newly inserted into the system and placed in an insert category, having, by definition, no active data on the logical volume.
As described in commonly assigned U.S. Pat. No. 5,546,557, host systems have programming allowing them to eject data storage volumes that are no longer needed in a data storage device, when they are operating with an individual data storage device in native mode. But there is no present method that would allow the host system to eject a logical volume from a data storage subsystem by guaranteeing that an ejected logical volume is no longer active or needed.